Mikheil Saakashvili, a former Georgian president and ex-governor of Ukraine's Odesa region, said on September 11 after forcing his way into Ukraine that he wants to get involved in Ukrainian politics again and help unite Kyiv's opposition.

"I want to say that this is the beginning of my fight," Saakashvili said at a press conference in Lviv after illegally crossing into Ukraine from Poland a day earlier despite warnings from Ukrainian authorities that he faces "serious" criminal charges.

"I am fighting against rampant corruption, against the fact that oligarchs are in full control of Ukraine again, against the fact that the Maidan has been betrayed," he said. "We should have democracy in our country and should not have the diktat of the oligarchs."

Saakashvili said he would travel to all regions of Ukraine to unite "different political forces around a common theme that we must have a democracy and we should not let oligarchs hold sway."

Saakashvili has said he was stripped of his Ukrainian citizenship by his one-time ally Ukrainian President Petro Poroshenko because Poroshenko views him as a threat. But he said on September 11 that he does not want the presidency for himself and wants to promote a new, younger politician to the post, the Reuters news agency reported.

Saakashvili was joined as he crossed the border by Yulia Tymoshenko, a former prime minister and leader of one of Ukraine's largest opposition parties. She currently is ahead of Poroshenko in public opinion polls, Reuters reported.

Reuters also reported that reformist lawmaker Mustafa Nayyem, one of the leaders of the Maidan protests and a member of Poroshenko's faction in parliament, traveled with Saakashvili and has accused Kyiv authorities of trying to silence opponents.

"We didn't want this country when we stayed on Maidan," Reuters quoted Nayyem as saying. "We wanted a country in which opponents, political opponents, have a right to say what they want."

Ukrainian Interior Minister Arsen Avakov had earlier called the border breach by Saakashvili "an attack on the state's basic institutions" and said all those responsible should turn themselves in.

A criminal investigation was launched against Saakashvili after he defied Ukrainian authorities and returned to the country that stripped him of citizenship in July.

Poroshenko chided Saakashvili for crossing the border without proper documents. He said Saakashvili should have contested the decree stripping him of Ukrainian citizenship in court if he disagreed with it.

Saakashvili said in Lviv that he no longer had a Ukrainian passport, claiming it was "stolen by police" from a bus that had transported him into Ukraine.

Besides running the risk of being arrested for illegally crossing into Ukraine, Saakashvili also faces possible extradition to Georgia where he is wanted on charges of misappropriating property and abusing his office during his nine years as Georgia's president. Saakashvili says those charges are politically motivated.

Saakashvili lost his Georgian citizenship in 2015 when he was granted Ukrainian citizenship in order to take up Poroshenko's offer to become governor of the Black Sea region of Odesa. Tbilisi does not allow dual citizenship.

Saakashvili resigned from the Odesa governor's post in November 2016, complaining he had been blocked from carrying out reforms.

In July, Poroshenko stripped Saakashvili of his Ukrainian citizenship amid a falling out between the two former allies.